1. Field of the Invention
The present invention relates to the field of the rehabilitation of soils, and more specifically to the field of the rehabilitation of polluted soils by means of a third substance (generally--liquid).
Polluted soils constitute a heterogeneous system in which the polluted substance and the pollutant have a fundamentally different chemical nature. Indeed, the polluted substance has an essentially mineral nature while the pollutant has an essentially organic nature.
The third substance has a selective affinity for the pollutant and can thus advantageously be used to wash the polluted substance.
Should the third substance be a solvent, then a homogeneous, monophase solution would be obtained wherein the pollutant is the solute, the whole entity consisting of the polluted substance and the solution then forming a decantable biphase mixture.
2. Description of the Prior Art
Most of the methods used in the prior art consist in carrying out a washing of the polluted soils by percolation according to which the third substance, which is sprayed over a vessel containing the polluted soils, infiltrates these soils and is then recovered at the bottom of the vessel in the form of a polluted solution.
Such methods are slow because they achieve very mediocre quality contacting between the third substance and the polluted soils. Consequently, the extraction is done badly, and the depollution efficiency is low in relation to the quantity of third substance introduced. Furthermore, the infiltration of the third substance into the polluted soils is done along a preferred path sidetracking certain zones of the percolation vessel.
Certain methods, on the contrary, consist of an operation of washing by the mixing of the polluted soils and of the third substance in a mixing vessel.
Vigorous shaking promotes contacting but prompts an attrition of the soils generating fine particles that have to be processed with care.
Furthermore, these methods are discontinuous and call for a separation of the washed soils and of the pollutant solution obtained after the extraction of the pollutant. This separation is done in a subsequent step, by decantation.
Furthermore, the prior art methods generally call for equipment that cannot be used on the sites of the pollution. For example, the methods mentioned here above include notably percolation vessels or decantation vessels whose dimensions are such that they generally cannot be transported.